Loud-speaker and driving motor therefor



Nov. 29 1940. J. P. QUAM LOUD-SPEAKER AND DRIVING MOTOR THERFOR Filed May 3l, 19158 2 Sheets-Sheet l LOUD-SPEAKER AND DRIVING MOTOR THEREFOR Filed May 31, 1938 2 Sheets--Shee'rl 2 Patented Nov. 26, 1940 UNITED STATES PATENT OFFICE:

LOUD-SPEAKER AND DRIVING MOTOR THEREFOR of Missouri Application May 31, 1938, Serial No. 210,934

8 Claims.

My invention relates in general to sound devices, and more in particular to a loud-speaker of the so-called magnetic type and the driving unit `for such speaker.

Magnetic speakers, as represented by loudspeakers with a moving iron-type driving unit, offer numerous advantages from the standpoint of original cost, and cost of operation, weight, and size, over so-called dynamic speakers having a moving-coil type driving unit. The dynamic speakers, although having the disadvantages in comparison to the magnetic speakers discussed above, have in the past had a marked advantage from the standpoint of delity and volume of reproduction.

The advantages in the dynamic speaker result primarily from the necessary mechanical construction of the two types of speakers, with the construction of the dynamic-type speaker making possible a greater amplitude of vibration for the diaphragm. In the past the amplitude of vibration of the diaphragm of the magnetic speaker and the moving elements of the driving unit for such diaphragm has been limited by the size of the area within which the moving elements can operate without striking iixed members such as the pole pieces. This space within which the moving elements can operate is called an air gap. As the air gap is increased in size to permitv substantial movement in the moving elements, losses are introduced in the magnetic circuit for the moving element which seriously reduces the operating efficiency of the speaker evidenced primarily in a loss in sensitivity in the speaker. As is known, the greatest amplitude of vibration occurs on the low notes or on the low sound frequencies, and in the past, due to the diiculties discussed above, the reproduction of the loud low notes is proportionately limited. If an attempt is made in the driving unit to compensate for the loss in responsiveness to low note impulses, by increasing the number of turnsl of the coil providing a magnetic field at the pole piece for the moving element, such increase in turns normally acts merely to emphasize the high notes or high frequencies. This destroys fidelity of reproduction over all sound frequencies reproduced. Structure intermediate the moving elements of the driving unit of the magnetic speaker and the diaphragm of the speaker has been used to step up the ratio of movement of the diaphragm to the moving element so that a greater amplitude of vibration of the diaphragm could be secured with a relatively small amplitude of vibration of the moving element, thus overcoming some of the mechanical disadvantages of a small space within which the moving element could operate. However, there are mechanical limitations in the step-up structure beyond which distortion occurs in translating movement of the moving element into movement of the diaphragm, and in addition, by virtue of necessary losses in the magnetic circuits of many of the prior speakers forces were insuilcient to operate the step-up structure satisfactorily beyond certain mechanical limitations. Some of the magnetic losses were overcome by utilizing a relatively expensive construction for the entire motor and a heavy laminated moving element in the motor, but this expedient was not entirely satisfactory.

A further diiiiculty for the magnetic-type speaker as contrasted to the dynamic type, arose because the lower cost magnetic-type speakers could not be used in inter-office communicating systems and the like.

Many of these diiiiculties are not peculiar alone to loud-speakers employing a vibratory motor, but to all applications for vibratory units with a moving element or armature and a magnetizable member for moving such element with a vibrating motion. This is particularly true as far as providing enough metal in the armature for a good iiux path, and overcoming or counteracting magnetic losses at an air gap or space for movement of the armature, are concerned.

An object of my invention is to provide an improved vibratory motor.

A further object of my invention is to provide an improved loud-speaker of the so-called magnetic type.

A further object of my invention is to provide an inexpensive, light-weight loud-speaker of the magnetic type which has substantially the same sensitivity and volume output as a dynamic-type speaker.

Another object of my invention is to provide a magnetic circuit in a vibratory motor. wherein the elements in such circuit provide a good magnetic path and the losses are relatively low. 'I'his has been accomplished in the various embodiments of my invention by means of a moving unit or armature of a magnetic material, including a mounting plate and a plurality of individual metal parts rigidly secured to said mounting plate with a surface area substantially the same as the mounting plate. 'I'he metal parts are secured on the mounting plate in a manner to provide flexibility intermediate the ends of such unit for hinge-like action therein yet avoid undue flexibility over the entire unit and rattling therein. These parts are provided in good mag- .netic material relatively large in cross-section, with low reluctance and accommodating a large number of lines of force or magnetic ux. A moving unit of this construction has been found to be responsive to speech current impulses over the entire normal operating range so as to provide extreme sensitivity in such unit over such range, and in turn provide a high fidelity of reproduction.

Another feature in the vibratory motor of my invention is the provision of a moving unit or armature which is continuously magnetized so as to assist the forces of attraction acting upon the same to move it.

It is also an object of my invention to provide a frame and driving unit for a cone-shaped diaphragm for a loud-speaker of such shape and size .as to materially reduce the normal depth of the speaker at the axis of movement of the diaphragm, and thus reduce the necessary space required for mounting such speaker in a cabinet or the like.

A still further object of my invention is to provide a loud-speaker having a high-power driving unit, yet of such light weight and simplied construction that the normal structural mounting requirements for the speaker are simplied and reduced'in cost.

Another object of my invention is to provide a magnetic-type loud-speaker which is equally suitable for use as a microphone as it is as a sound reproducer.

Other objects, features, and advantages of my invention will be apparent from the following description taken with the drawings, in which:

Fig. 1 isa rear View of a loud-speaker embodying my invention.

Fig. 2 is a side elevation thereof.

Fig. 3 is an enlarged detailed fragmentary illustration of the armature in themotor of Figs. l and 2, along the line 3-3 of Fig. 1.

Fig. 4 is an illustration similar to Fig. 3 of a modification of the armature for the motor.

Fig. 5 is a similar illustration of a still further modification of 'the armature for the motor.

Fig. 6 is a fragmentary rear View of a loudspeaker in accordance with a modified embodiment of the invention.

Fig. 7 is a side elevation of the speaker of Fig. 6.

' Fig.8 is a fragmentary and somewhat schematic illustration in vertical section of the vibratory motor of Figs. 6 and 7.

Fig. 9 is a somewhat schematic illustration of the pole pieces, coil, and armature, of the motor of Figs. 6 to 8, and showing also a portion of the magnetic circuit therefor.

Fig. 10 is an illustration similar to that of Fig. 9 of the motor of Figs. 1 and 2.

Referring now to the drawings, a loud-speaker is illustrated in Figs. 1 and 2 having a movable cone-shaped diaphragm II supported along its edge from the annular open front face of a stamped-out frame or basket I2 having an open frusta-conical back portion. The back portion includes a pair of legs I3 and Il separated at their rear ends to permit the apex portion I6 of the cone I I to extend therethrough. A mounting plate I1 of magnetic material is rigidly secured, by welding'or the like, to the ends of the legs I3 and I4 of the frame as shown clearly in Fig. 2. An aperture I8 in' the mounting plate I'I accommodates the apex I 6 of the cone.

The cone-shaped diaphragm II is driven by a vibratory motor including a permanent magnet I9 which may desirably be of the size and shape shown in Figs. l and 2, which illustrations are taken directly from a commercial embodiment of the invention, and are full size. Cavities 2I on each. side of the permanent magnet I9 accommodate mounting screws 22 for rigidly securing an armature 23 of magnetic material with the magnet I9, to the mountingl plate I1. The armature 23 is vibrated in accordance with the impulses of a unidirectional pulsating current energizing coil 24 supported on the central leg 26 (Fig. 10) of an E-shaped pole member 2l having outside legs 28 of such a height as to normally extend substantially flush with or above the top surface of the armature 23 and spaced from such arma-ture sumciently to provide an air gap intermediate each leg 28 and the corresponding side of such armature. These air gaps are merely large enough to provide free vibratory movement of the armature.

The armature 23 acts through a knife-edge driving arm 3l soldered or otherwise rigidly secured thereto and a driving rod 32 secured to the arm 3l. A substantially L-shaped tensioning device and step-up member 33 is secured at one end to the mounting plate I1, and extends at the other end over the apex I6 of the cone to receive a stylus or driving rod 34 connecting such step-up member with said cone. The driving rod 32 is rigidly secured to the horizontal portion of the member 33 at a point intermediate the ends thereof and the entire member 33 pivots about a fulcrum at its mounting portion on the plate Il. The particular point at which the rod 32 is secured to the member 33 is such that the ratio of movement of the armature 23 to the diaphragm I I is suicient to provide the desired amplitude of vibration for the diaphragm with a relatively small movement of the armature in the air gap as will be described. With the pole piece and permanent magnet mounted upon the plate I'I at one side of the aperture I8, and the step-up member at the other side, yet overhanging the aperture, the apex portion I6 of thediaphragm is extended through the aperture so as to reduce the normal depth of the speaker along the line of movement of the diaphragm. The reduced depth of the diaphragm frame or basket, of course, reduces the space requirements for mounting the speaker which is especially desirable in the small cabinet radio receivers, and in the automobile radio receivers Where space is an important factor. Furthermore, it has been found that improved operation of the step-up member 33 is provided with such member secured to the mounting plate at an end oppositely disposed to .the mounted end of the armature, as contrasted to a mounting thereof so that the free end extends in the same directionv as the free end of the arma-ture.

As to the detailed description of the driving unit or vibratory motor for the loud-speaker, the permanent magnet I9 is preferably provided in a material consisting of an alloy of aluminum, nickel, and iron. This material is a comercial product known as Alnic, and provides a magnet of great strength for a relatively small volume of metal. In one commercial embodiment of the invention illustrated herein the permanent magnet I9 of this material weighed approximately two ounces. The pole piece 21 for the driving unit consists of a plurality of steel laminations, each of which is cut in an E-shape and isoI secured together into an integral-like member by means of rivets 36 or the like. The center leg 26 of the pole piece is of such a length with reference to the outside pole legs 28, as to permit the desired amplitude of vibration in the armature 23 above the leg, and yet in its position of rest the top surface of the armature 23 is substantially flush with the top of the pole legs 28 or slightly below such top. A prewound coil 24 on a spool ls inserted over the center leg of the pole piece, and is adapted for connection into a radio receiver or other electrical circuit for which the loud-speaker is adaptable. The windings on the coil 24, are, of course, in such a direction as to provide the desired polarity at the top of the center leg 26 for attraction of the armature 23. Although, of course, the direction of current flow through the coil can be changed by merely reversing the connection for the leads 31 and 38, if the rst connection thereof does not provide the desired polarity in the pole piece.

The armature 23 is provided in such a width that there is a slight air gap intermediate each side thereof, and the corresponding adjacent pole leg 28 to permit free vibration of such armature. With the pole legs 28 of such length as to lie immediately adjacent the sides of the armature, the magnetic return path as indicated by the arrowed lines in Fig. is substantially entirely through metal, thus reducing the normal reluctance of prior motors where the return path included wider air spaces. Similarly an air gap is provided intermediate the top of the center leg 26 and the armature 23 when the latter is in a position of rest, and although there must be sufficient space intermediate such leg 26 and the armature to permit a relatively great amplitude of vibration thereof, at the same time it is desired to keep this gap at a minimum so as to maintain as low a magnetic loss as possible at the gap. In the magnetic circuit of the present invention, however, the magnetic flux possible in the circuit is so much greater than that in the prior devices of this general nature due primarily to the construction of the armature and the pole piece, that the flux density at the gap intermediate the leg 26 and armature 23 remains large even with a relatively large gap. In the preferred construction of the armature 23, as illustrated in detail in Fig. 3, a one-piece mounting plate 4| of flexible magnetic material is provided of the size and shape shown in the illustration of Fig. 1, and has secured thereto on the under side thereof, a pair of rigid metal plate members 42 and 43. These plate members butt against one another at their inside edges to form a joint at 44, and are welded to the plate 4| at a plurality of points as indicated by the rough cross-hatching as W in Fig. 1. I have found that it is desirable to weld the elements 42 and 43 onto the plate 4| along two lines each spaced from the joint 44 approximately oneeighth of an inch, thus providing approximately one-quarter inch of free bendable space intermediate the lines of the welds. Other welded points are promiscuously applied over the remainder of the surface of the armature so as to secure the elements 42 and 43 to the plate 4| in a manner to prevent rattling or vibration.

The under surface of the element 42 of the armature is pulled tightly against the top surface of the permanent magnet |9 by means of the screws 22 extending through tapped apertures or having a nut thereon at the mounting plate l1.

The magnet I9, of course, is originally magnetized so that the top of the magnet is of one polarity and the bottom of the magnet is of an opposite polarity. As mentioned above, the permanent magnet i9 is highly magnetized and with the armature 23 being provided in a. good magnetic material such as silicon steel, there is a very good ux path through the armature from the magnet. This is readily evident when it is considered that, in one instance, I provide the plates 42 and 43 .062 inch in thickness, and the plate 4| to which the elements are welded is .028 inch thick, With the heavy metal portion of the armature, namely, the plates 42 and 43 on the underside, the shortest flux path over the' magnetic circuit is through the portion having the least reluctance, thus improving the overall efliciency of the circuit. Assuming that the north pole of the magnet I9 is at the top, while the south pole is at the bottom, in engagement with the mounting plate, the armature 23 is polarized as a north pole, while the mounting plate I1 and the pole piece 21 in the magnetic circuit with the bottom of the magnet I9, are south poles.

As mentioned above, the leads 3l and 38 for the coil 24 are so connected that the current flow through the coil is in a direction such as to provide the lines of force in the magnetic field around the coil passing in a desired direction. This direction, of course, determines the polarity at the opposite ends of the magnetic field and in the present invention the polarity at the top of the magnetic field corresponds to the polarity at the top of the pole leg 26. In other words, the magnetic field at the top of the pole leg 26 is supplemented by the superimposed magnetic field around the coil 24, and with a south pole for each of the magnetic fields at the top of the pole leg 26, the force of attraction on the armature 23 is materially increased. At the same time the induced magnetic field in the pole leg 26 provides a north pole at the bottom of the pole leg 26 to in effect neutralize the magnetic lines of force of the opposite polarity in the outside pole legs 2B. The force of attraction between the top of the pole leg 26 and the magnetized armature 23 is so great that the armature is attracted with each current impulse through the coil. The mounted end of the armature 23 Aon the magnet I9, of course, remains rigid, but as the armature is attracted to the top face of the pole leg 26, such armature bends at the point 44 substantially in a hinge-like action, and due to the particular construction of the armature as described above, marked flexibility is provided for such a relatively large amount of metal.

With the armature 23 continuously magnetized, and being'of a polarity opposite to that of the top portion of the pole leg 26, a weaker current impulse with a resultant weaker magnetic-field at the gap will still attract such armature and cause a corresponding movement of the diaphragm so that sound is reproduced over a wide range of voice current frequencies. The movement of the armature 23, of course, is transmitted through the connecting mechanism including the knife-edge arm 3| and the step-up member 33 to the diaphragm Il.

A modification of the armature is illustrated in Fig. 4 wherein an enlarged fragmentary Adetail of an armature |23 is illustrated having a mounting plate |4| intermediate a pair of metal elements |42 and |43, on the upper side of the mounting plate I 4| and corresponding elements |42' and |43 on the lower side of the plate |4|. The elements |42 and |43 as well as their counterparts |42 and |43 areof the same size and shape as the corresponding elements 42 and 43 in the structure of Fig. 3. However, the elements |42`and |43 as well as |42' and |43' are, in one commercial embodiment of my invention, .050 inch thick rather than .062 inch thick, as are the plates 42 and 43. 'I'he bi-part elements are welded to the mounting plate |4| in the same manner as previously described. In the particular embodiment mentioned, the plate |4| is .025 inch thick.

A still further modication oi the armature structure is illustrated in Fig. 5 with the metal elements 242 and 243 secured intermediate a pair of mounting plates 24| and 24| of a size and shape identical with the complete surface area on one face of the armature 23 illustrated in Figs. 1 and 2. 'I'he same relative position for the welded spots is provided in the armature 223 as described with reference to the armature 23. In one adaptation of this structure, the plates 24| and 24|' were each .010 inch thick and the elements 242 and 243 were each .040 inch thick.

A modication of the vibratory motor is illustrated in Figs. 6 to 9, inclusive. 'I'he elements of this motor remain substantially the same as for the motor of Figs. 1 and 2 except the pole piece. As a result of the modification in the pole piece the configuration of the armature is changed. The laminated pole piece 46 of the modied embodiment comprises an E-shaped portionwith outer legs 41 and an inner pole leg 48 all identical with the pole piece 21 shown in Fig. 10. The armature 23 vibrates in an air gap provided intermediate the top face of the pole leg 48, and the under face or surface of a bridge-like, pole-piece portion 49 extending across the outer legs 41 and rigidly secured thereto by soldering or the like. A coil 24 is supported on the center pole leg 48 in thel manner previously described. f

In this embodiment the magnetic return path is through the air gap intermediate the bridge portion 49 and the pole leg 48 and through the armature in the air gap as shown by th arrowed lines in Fig. 9. As a result the forward or vibratory portion F of the armature is restricted in width as can be seen in Figs. 6 and 9. The metal removed from the sides, so to speak, is

added at the front to extendy the length of the armature and this permits a shortening of the driving arm 3|. and 8 that the highest point on the driving arm 3| is substantially iush with the top face of the bridge portion 49 or slightly below the same. In packing the speakers, the bridge portion thus protects the driving arm 3| and consequently the armature from injury when a packing board or the like rests upon the bridge portion. 'I'his same holds true in the assembly of the speaker into a cabinet or onto a receiver chassis. The construction of the armature 23 as illustrated is similar to the armature 23, except for the change in conguration of the elements 4|', 42 and 43', as is readily apparent from Figs. 6 and 9.

As can be understood, from a consideration of Figs. 8 and 9, with the south pole of the magnet |9 in engagement with the mounting plate |1 of magnetic material, the entire pole piece 46 including the bridge portion 49, is also a south pole. At the Sametime, the armature 23' is It can be noted from Figs. 7

magnetized to have a polarity corresponding to the top oi the magnet |9, or a north pole, so that the armature 23', as a north pole, lies intermediate the two pole faces of the portions 48 and 49 which are both south poles in the absence of a4 current through the coil 24. 'Ihe leads 31 and 38 for the coil 24, are connected so that the voice currents will pass through the winding in a direction such that the direction of the lines of force in the magnetic eld around the coil provide a south pole at the top of the pole leg 48, while the bottom of the leg becomes a northv pole. The magnetic forces set up in the pole leg 48, as a result of the energization of the coil 24, pass through the outside pole legs 41 and the bridge 49, as indicated by the lines and arrows in Fig. 9, and the polarity of these latter portions correspond to that of the bottom of the pole leg 48. These magnetic forces tend to counteract or overcome the original magnetic forces in the outside pole legs and bridge in the opposite direction, so that with each voice current impulse in the coil 24, the magnetic forces at 49 are substantially neutralized, or the bridge portion becomes a north pole, depending upon the strength of the magnetic field set up around the coil. Therefore, with some or possibly all impulses of the current through the coil 24, the armature 23 is repelled from the pole face at the bridge portion 49, and, of course, is simultaneously attracted by a greater magnetic force, to the pole face at the top of the leg 48. The operation of this magnetic circuit is such as to cause movement of the armature 23' on the slightest impulse through the coil 48, and with the movement transforming structure illustrated in Fig. '1, and described-above, a small movement in the armature 23 can be translated into a relatively great amplitude of vibration in the diaphragm so that a substantial volume of reproduction is obtained. That is, this motor structure provides for an extremely sensitive operation.. yet does not require so Wide an air gap intermediate the pole leg A48 and bridge portion 49 to permit the armature to accurately respond to the current impulses, that magnetic losses are introduced at the air gap which cut down the eiciency of the motor. In commercial embodiments ofthe invention I have provided an air gap of .012 of an inch to .015 of an inch on top of and on the bottom of the armature 23', with a similar range in the air gap at the bottom of the armature 23 in Figs. 1, 2 and 10.

It is understood that the modified embodiments of the armature as illustrated in Figs. 4 and 5 may be substituted for the armature 23 in the motor of Figs. 6 to 9, inclusive.

The embodiments of my invention, described above, have also been found to act as extremely sensitive microphones when used in inter-ofiicecommunicating systems and the like, where two or more loud-speakers with an intermediate The movement of the amature 23 induces a current in the coil 24 which is carried through an intermediate amplified system to be reproduced in one or more speakers in connection therewith.

From the above description, it is apparent that I provide a simple, inexpensive vibratory motor, and loud-speaker of the magnetic type which is light in weight and relatively smallin size. As a result of the mechanical construction of the motor and speaker, and the magnetic circuits as described with respect to the two embodiments Y of the invention, reluctance in the circuits is a minimum and a large magnetic force may be accommodated in any one of the armatures in the magnetic circuit before reaching saturation. As a result, the magnetic forces inthe circuit are efficiently applied, and extreme sensitivity, as well as operation over a wide range of voice frequencies is obtained. Furthermore, the rattling and vibrational `noises present vin the prior art speakers of this type, are overcome byvirtue of tne armature construction, and lthe magnetic forces acting upon the amature.

Although I have illustratedvand described my invention in its preferred embodiments, it is understood that the invention is notl limited thereto, but is limited only by the scope of the appended claims.

I claim:

l. A vibratory armature for electrical apparatus including a one-piece metal mounting member and a pair of metal elements irremovably secured to said mounting member and substantially abutting one another at one end of each to provide a substantially closed joint therebetween intermediate the longitudinal'ends of the mounting member, with said mounting member being bendable at said joint formed by said metal elements. l

2. A vibratory armature for electrical apparatus including a one-piece metal mounting member having a top surface and a bottom surface, a pair of metal elements irremovably secured to the top surface oi' said mounting member, and a second pair of metal elements irremovably secured to the bottom surface of said mounting member, with each of said pairs of metal elements substantially abutting one another at corresponding ends thereof to provide a substantially closed joint therebetween intermediate the oppositely disposed ends of the mounting member, with the substantially closed joint between one pair of metal elements lying above the similar joint between the other of said metal elements, and with said mounting member being bendable .at a portion coresponding to the two joints formed by said metal elements.

3. A vibratory armature for electrical apparatus including a pair of one-piece metal members spaced apart from one another, a pair of metal elements between said metal members and irremovably secured to each member, with said metal elements positioned end to vend with respect in one another and together occupying an area substantially the same as vthe surface area of one of said metal members, saisiv amature be^ ing flexible at a portion corresponding to the juncture of said metal elements, and relatively 7 non-iiexible over the remainder of the area thereof. y

4. A plate-like armature for electrical apparatus, including a plurality of metal members irremovably secured together, at least one `oi? said members extending substantially the length of l the armature, with the remainder of such members being of such shape and conguration and so secured with relation to one another and to said one member that said armature is flexible ture, and with said armature `being relatively non-flexible over the remainder of its entire area.

5. An armature for a vibratory motor comprising a one piece mounting member extending substantially the length of the armature andl a plurality of relatively noniexible metal members of low reluctance thereon, with some of said metal members being welded to said mounting member and substantially in abutting position to the remainder of said metal members, and said mounting member being bendable only at .a transverse portion corresponding with said substantial'abutment of said metal members, said metal members and said mounting member maintaining a highly conductive magnetic ux path V`through the armature during the bending thereof.v Y

6. A vibratory armature for electrical apparatus comprising a mounting member of magnetic material, a plurality of metal elements lirremovably secured to one' end of the mounting member, and a plurality of additional metal elements secured to the other end thereof, with the metal elements at one end substantially abutting the metal elements at the other end and providing a substantially closed joint at such substantial abutment, with said armature being bendable at such substantially closed joint and relatively non-:dexible over the remainder thereof.

7. A vibratory armature for electrical apparatus comprising a mounting portion for normal rigid mounting and a vibratory portion extending therefrom for vibratory movement, with said armature being non-flexible at said two portions, and flexible at a transverse line intermediate said portions, said armature including a relatively iiexibie metal member extending into each of said portions and having a pair of relatively non-flexible metal elements welded thereto at the mounting portion and an additional pair of relatively non-exible metal elements welded thereto at the vibratory portion, with one of said pairs of metal elements substantially abutting the other of said pairs and the transverse line oi' ilexibility of the armature being coincident with said substantial abutting portion for said pairs of metal elements.

8. In a magnetic type loud-speaker having a vibratory motor for driving the diaphragm of such loud-speaker, a vibratory amature for said motor having a bendable mounting member extending substantially the length of said armature. a pair of metal members secured to one face of said mounting member and being in end to end substantially abutting relationship. and a corresponding pair of metal members similarly secured on'the other face of said mounting member with said metal members acting to corinne thebendmetal members.

JAMES P. GUAM..

of the 

